Among the electronic measuring apparatuses, for example those for measuring linear dimensions of mechanical workpieces, there can be distinguished two types of relatively simple apparatuses--insofar as the type of measurements and processings are concerned--, i.e. "column" or "dial" type apparatuses, or comparators.
The column apparatus comprises a display unit (normally also acting as a power supply, detector and processor) with a substantially right parallelepipedon shaped casing, considerably smaller in width with respect to length and depth. At least two display devices--one of the analog and the other of the digital type--and a programming and control keyboard are arranged at a front face of the casing having dimensions corresponding to the aforementioned length and width. Electric connectors are arranged at a rear face of the casing, and provide connection, by means of cables, with the electric power supply network, input devices, more specifically one or more measuring heads, and output devices, like relays, additional measurement signal processors, etc. The analog display device, for example of the light emitting diode (LED) type or with segments consisting of small gas discharge tubes, is generally arranged along the length of the front face, substantially as a vertical scale, while the digital device, usually of the light segments type, is arranged along the direction of the width of the front face. In fact, typically the socalled "electronic columns" are vertically arranged and rest on a table or on a support plane by means of legs clamped to a lower base of the casing.
There are also known apparatuses, deriving from the column-type ones, arranged horizontally and resting on a table or a support plane, in which both the display devices are arranged in a horizontal direction.
These electronic columns are rather bulky and, in the event a plurality of vertical columns are arranged side by side (or horizontally arranged apparatuses are superimposed one upon another) for the display of a plurality of measurements relating to the same workpiece, the overall dimensions may give rise to inconveniences, such as the need to arrange the columns at a considerable distance from the associated measuring heads and the difficulty in readily and accurately viewing the various measurements on display.
The so-called "dial-type" electronic comparators, or similar ones, like the comparator disclosed in U.S. Pat. No. 4,289,382 and the one disclosed in European patent EP-B-0097520 are considerably more compact. These comparators comprise a display unit with a substantially cylindric casing, of small thickness, or a substantially prismatic casing. At a front face of the casing there are arranged two display devices, one of the analog and the other of the digital type. Some keys, or a keyboard, are located at the same front face of the casing, or at its lateral surface (annular surface, or rectangular faces). A measuring head, more specifically a measuring head of the so-called "cartridge type", can be directly coupled, by means of a mechanical coupling, to the casing of the display unit, or it can be-remotely located and thus connected via cable to the display unit.
The dial comparator is typically coupled to an external support by means of a locking device that, in the case of a comparator with an integrated measuring head, is coupled to the head casing.
In relatively simple measuring benches it could be desirable to use measuring heads with integrated display units. For example, in a measuring bench for checking a plurality of diameters of shaft-like workpieces, manually positioned in the measuring position, it could be desirable to arrange the apparatuses (with integrated measuring heads) side by-side according to the shaft axis direction. The known dial type comparators are not always fit for performing this; for example, when it is required to check diameters at several closely spaced apart cross-sections of the shaft. Under such a circumstance the overall dimensions of the front faces of the display units can render impossible this arrangement and apparatuses with remote measuring heads must be used, as disclosed in European patent EP-B-0097520. However, also for this arrangement, the overall dimensions of the front faces of the display units do not enable to achieve a compact and easily readable display group.